A composite multilayer film is frequently used in order to satisfy the various performances required for a packaging bag and a packaging container used to pack foods, medicinal products, and the like. The aforementioned packaging bag is a bag-like product which is obtained by heat-sealing the side surfaces of a folded or layered multilayer film. Furthermore, the aforementioned packaging container is a container-like product which is obtained by heat-sealing a bottom member and a lid member, said bottom member being formed in a shape suitable to the contents through vacuum forming or pressure forming of a multilayer film, said lid member being an unformed film.
The multilayer film used for a package body, such as a packaging bag and a packaging container, is required to have an impact resistance, flex resistance, and anti-pinhole property. The anti-pinhole property is necessary for preventing the occurrence of pinholes in a package body, said occurrence being caused due to the external stress exerted on the package body as a result of vibrations or falls, for example, during the distribution process. Additionally, when a package body is used as an inner bag of a bag-in-box in which mostly a substance with a high flowability, such as a fluid, is filled in, or when contents having an unfixed shape or a sharp part are to be packed in a package body, the package body is often required of an anti-pinhole property higher than usual. A multilayer film including various stretched films or a polyamide resin is used favorably as a multilayer film having an anti-pinhole property (for example, see Patent Literature 1).
Furthermore, in a package body, the impact resistance, flex resistance, and anti-pinhole property required depending on the contents to be packed differ. Therefore, among the multilayer films used for a package body for packing heavy objects and the like, those within the range of a thickness belonging to the sheet category according to the JIS classification may be used.
Recently, in order to reduce the environmental burden, it is desired to decrease the thickness of the multilayer films used for package bodies than the thickness of conventional multilayer films. Therefore, various attempts are being made to reduce the thickness than the conventional multilayer films by changing the configuration of the multilayer films (for example, see Patent Literature 2).